An immobilizer is used as one of vehicle anti-theft devices. The immobilizer provides wireless communication between an onboard device and an electronic key (mobile device) that stores a key ID unique to each vehicle.
The immobilizer collates a key ID received from the electronic key with a key ID stored in the onboard device and allows an engine to start only when both key IDs match.
A system that provides an expiration date to authenticate the key ID (see patent literature 1) in a case where the electronic key is stolen or duplicated is proposed. In order to update the expiration date, the onboard device used in the system periodically communicates with a server managing the expiration date with an onboard communication device and receives authentication from the server.
However, the expiration date may pass when a user parks the vehicle outside range to be incapable of connection to a mobile communication network. In this case, the onboard device cannot communicate with the server using the onboard communication device, and therefore the onboard device cannot update the expiration date. To be prepared for this case, the system allows a registered mobile terminal device owned by the user to be used an alternative device to the onboard communication device. The user owning the mobile terminal device moves to an area capable of connection to the mobile communication network, receives update information from the server, returns to the vehicle, and transmits the update information to the onboard device to update the expiration date.